It should be possible to get it (suffucient) watertight, I have capsized my (previous) Taipan 4.9 at least ten times <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />, never complete turtle but also never water in the mast. It was always possible to right the boat single handed, so if there was water in it, it would be a little bit.

But I noticed on my Blade (same mast section) that after just one capsize there was some water in it, and it took a couple of weeks before it was gone. Just a capsize, not going turtle. You might have a look at the Taipan setup

Geert